FIG. 1 depicts some parameters associated with a few existing and emerging standards for wireless connectivity. Based on targeted range and supported data rates, these standards can be grouped into four categories: Wireless Wide Area Networks (WWAN), Wireless Metropolitan Area Networks (WMAN), Wireless Local Area Networks (WLAN) and Wireless Personal Area Networks (WPAN).
An example of a Wireless Local Area Network (WLAN) is an 802.11x (x=a, b, g, n, etc.) network. An 802.11x NIC (network interface card) or 802.11x built-in circuitry might be used for networking an electronic device to the outside world, or at least to devices at other nodes of a WLAN 802.11x network.
The 802.11x specifications uses unlicensed, free spectrum in either the 2.4 GHz or 5 GHz frequency bands, supporting data rates of up to 54 Megabits per second (Mbps) and ranges of 300 feet and more. The 802.11x standard, also known as Wi-Fi, was adopted several years ago, and is now being widely deployed for WLAN connectivity in homes, offices and public places like airports, coffee shops and university campuses.
The adoption and deployment of 802.11x-compliant equipment has experienced tremendous growth in recent years. The majority of laptops manufactured today include a built-in wireless circuit compliant with some variant of the 802.11x standard. While originally devised for enabling wireless network connectivity (“wireless Ethernet”), WLAN connectivity based on the 802.11x standard is rapidly finding its way in new applications like mobile phones—primarily driven by the adoption of Voice-over-IP (VoIP)—and consumer electronics (home entertainment, video streaming etc.). In addition, with the development of the new 802.11xn specification, and the proliferation of citywide 802.11x deployment initiatives, the 802.11x standard is expanding into longer range applications.
FIG. 2 illustrates a typical 802.11x WLAN configuration in infrastructure mode 1. Although the 802.11x standard supports two modes of operation, namely ad-hoc mode and infrastructure mode, the infrastructure mode is used more often. In the infrastructure mode, a dedicated 802.11x wireless circuit, also called an access point (AP), is necessary for and manages an infrastructure network. AP 2 is configured specifically to coordinate the activities of the infrastructure network and to enable connectivity to, for example, the Internet or other WLANs via an Internet router 3, which may be disposed in AP 2. Other 802.11x-compliant wireless circuits, hereafter alternatively referred to as stations (STAs) 4 can become a member of the infrastructure network by going through an authentication and association procedure. Additional security procedures may be required as well. Once associated with the infrastructure network, a STA 4 can communicate with AP 2. A STA 4 may communicate with other STAs 4 of infrastructure network 1 via AP 2. Furthermore, a STA 4 may communicate with STAs of other infrastructure networks (not shown) via AP 2. On a regular basis, the STAs listen to the beacons and pending traffic from the AP 2.
In contrast to WLAN, no such unifying standard exists for WPAN. Instead, a number of proprietary and standardized communication protocols have been and are being developed for establishing short-range WPAN connectivity. Standardized protocols include the Bluetooth specification (based on the IEEE 802.15.1 standard), the recently approved Zigbee specification (based on the IEEE 802.15.4 standard), and the Ultra-Wideband (UWB) specification which is still under development. In addition, there are several proprietary protocols in the unlicensed 27 MHz, 900 MHz, and 2.4 GHz frequency bands developed for the sole purpose of providing short-range wireless connectivity. Examples include Cypress Semiconductor's proprietary wireless USB solution, or Logitech's proprietary FastRF solution. The lack of a unified standard is hindering the widespread adoption of WPAN technologies. In addition, several WPAN communication protocols co-exist in the same 2.4-GHz frequency band as a commonly used version of the WLAN protocol. Because they use different methods of accessing the wireless medium, and are not synchronized with one another, severe interference may result when devices conforming to such standards are made to co-exist and are positioned in the same physical vicinity.
One alternative for avoiding the above mentioned problems when seeking to establish interoperability between WPAN and WLAN networks, is to use network interface circuitry based on the WLAN protocol in WPAN STAs. However, the power dissipation of the resulting STA would be several orders of magnitude higher than what is acceptable in typical WPAN applications. WPAN technologies are typically used to establish communication with a remote battery-operated device for which it is inconvenient, impractical, or may be impossible to replace batteries. Examples include security sensors in windows, wearable or implanted medical monitoring devices or environmental sensors to monitor temperature, humidity or other environmental parameters. To minimize the frequency at which batteries need replacement, maximizing the battery life is of paramount importance, thus placing stringent requirements on the power that can be dissipated in establishing and maintaining the wireless communication link.
The power dissipation of a standard WLAN STA is several orders of magnitude higher than what is acceptable in most battery-operated devices for a number of reasons. First, in order to be able to communicate with the AP, which may be, for example, 300 feet away, a standard WLAN STA transmits at high transmit powers (up to 20 dBm) and is also required to receive relatively weak signals, attenuated heavily by the path loss it encounters in the over-the-air transmission. Second, the WLAN must adhere to stringent receiver sensitivity requirements. Both the transmit and receive requirements result in relatively large power dissipation in the network interface circuits. Furthermore, WLANs typically operate at relatively high data rates (up to 54 Mbps). It is thus undesirable to have a STA that is part of an infrastructure network to communicate at lower data rates, since such a STA will slow down the entire infrastructure network. This is the case because some of the communication between the AP and its associated STAs occurs at the lowest common data rate supported by all STAs. The noise and linearity requirements associated with transmitting at high data rates thus result in large power dissipation of the wireless 802.11x wireless circuit. Furthermore, there is significant protocol overhead associated with the services and procedures required to establish and maintain an association with an infrastructure network. This overhead translates directly in higher power dissipation. As a member of an infrastructure network coordinated by an AP, the STA has, on a regular basis, to listen to the beacons transmitted by the AP. Also, although the 802.11x standard specifies power save modes that allow the STA to skip some of the beacons, the STA is still required to wake up on a regular basis to maintain association and synchronization with the AP.
Accordingly, a need continues to exist for a method and apparatus that overcome the above-described problems and enable seamless integration of WPAN into WLAN infrastructure, and at power dissipation levels that meet the stringent requirements of battery-operated devices.